A maximum transmission unit (MTU) is the maximum amount of data that can be transmitted per unit of data. The MTU between a source and a destination of data is influenced by the protocols used to transmit that data. For example, tunneling protocols, such as Virtual Extensible Local Area Network (VXLAN) and Geneve, may be used to create a logical overlay network on physical network hardware. Logical overlay networks can be manipulated to be more dynamic to meet the needs of modern computing environments. The ability to redefine a logical network in that manner leads to dynamic logical networks being referred to as software defined networks (SDNs). SDNs, like the physical network interfaces on which they are implemented, have MTU requirements that are typically based on the protocols in use.
In particular, the tunneling protocol, or protocols, used to implement a SDN include their own network overhead or MTU requirements which may further reduce the size of a MTU for data traffic. For example, a data center may have a MTU of 9000 bytes while a tunneling protocol used between two endpoints within the data center requires 100 bytes of overhead. The MTU of the transferring endpoint would therefore need to be set to 8900 bytes to account for the tunneling protocol rather than the full 9000 bytes allowed by the data center. Moreover, the MTU may be different depending on which endpoints are involved. For instance, an additional tunneling protocol may be used to transport data between sites when two endpoints are located at different sites. If that additional tunneling protocol uses an additional 100 bytes of overhead, then the MTU at the transferring endpoint would need to be set to 8800 bytes. Likewise, the overhead required by some tunneling protocols may itself vary (e.g., Geneve allows for the carrying of information about an encapsulated packet and the metadata representing that data may vary in size depending on that information).
It may be possible for an administrator of an SDN to determine a minimum MTU size that would be imposed between two endpoints of the SDN and set the MTU at all endpoints to that minimum MTU size, otherwise, packets would be dropped along paths that do not satisfy the set MTU. However, larger MTUs are more efficient for transporting data. Therefore, the administrator would be undermining the efficiency of the SDN between endpoints that would otherwise be able to transmit using a larger MTU.